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Molecular and Cell Biology Practice Questions

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I am now in revision with 3 weeks before the exam for molecular and cell biology (together with another 3 subjects)
I would like to get model answers of past exam questions for part A (short questions) of my exam. There are 12 questions in part A in each past exam paper.

I have one of the past papers (part A) ready and attached.

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Since this is a sample exam, I presume that they're looking for succint, to the point answers. That's what I will try to provide, although where I think background knowledge is beneficial, I'll elaborate a bit more as well.

1) Name the components of the cytoskeleton, and how they're assembled.

Microfilaments - linear polymers of the protein actin.

Intermediate filaments - there are many types of IF's, so it's more useful to state that they are polymers of certain proteins in certain cell types. For example, skin cells have keratin IF's. These IF's can be in monomers, dimers or trimers, which often involves coiling of long strands of the basic protein unit strands together.

Microtubules - made of polymers of alpha and beta tubulin coming together using GTP as an enzymatic/energetic driver, typically at centrioles.

Why can cells with cytoskeletons be larger than those without?
The answer comes in the function of the cytoskeleton - they're ultimately support infrastructure. Akin to the steel rebar beams of a building, they provide structural integrity to the cell. As a result, a cell can greatly expand it's size without compromising structural integrity, whereas cells without cytoskeletons can literally stretch themselves too thin and lyse.

3) 3 ways phosphorylation can affect proteins:

1: the protein is directly phosphorylated, and in doing so, gains the energy to complete it's function.
2: another protein is phosphorylated and activated, and it's actions directly modulate the effects of our target protein (e.g. pRET leads to pERK)
3: phosphorylation of certain proteins can ultimately regulate the amount of expression of other proteins at the nuclear level.

3 different ways of lipid modifications:

1: Myristoylation - a myristoyl group is added at the N-terminus. It's hypothesized that the myristoyl group then binds to src, and the whole component is now capable of binding to certain enzymes on the cell membrane, which effectively localizes it to the cell membrane.

2: Palmitoylation - fatty acid attachment to cysteine (sometimes serine) residues. Various proteins that have undergone this are transported enzymatically by a myriad of different enzymes to the membrane.

3: Isoprenylation - describes the general addition of hydrophobic components to a protein. By doing so, the protein is transferred into the lipid membrane where the hydrophobic component ...

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The solution assists with answering model answers for molecular cell biology practice questions.

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Cell Biology Multiple Choice questions

1. Protein insertion into the mammalian ER membrane is typically
a. cotranslational c. pretranslational
b. post-translational d. quasitranslational

2. In N-glycosylation of proteins in the ER lumen, sugar(s) are added to the nascent chain at once.
a. 1 c. 7
b. 3 d. 14

3. All of the following proteins interact with exposed amino acids during protein folding in the ER except:
a. BiP c. PDI (protein disulfide isomerase)
b. calnexin and calreticulin d. prolylisomerase

4. Type I membrane proteins have all of the following properties except:
a. cleavable signal sequence c. internal stop-transfer sequence
b. internal signal-anchor sequence d. N-out, C-in topology

5. Proteins that do not fold properly in the ER lumen are degraded in the cytosol by
a. the etiosome c. the proteasome
b. the microsome d. the ribosome

6. Sorting of protein to mitochondrian and chloroplasts is
a. cotranslational c. pretranslational
b. post-translational d. quasitranslational

7. Tom/Tim and Toc/Tic protein complexes are involved in
a. post-receptor recognition events in the cytosolic folding of proteins prior to import into mitochondria or chloroplasts
b. pre-proteasomal steps in tagging aged proteins for degradation
c. protein translocation into mitochondria and chloroplasts, respectively
d. resetting biological clocks following rounds of intense protein synthesis

8. Protein sequences for targeting to mitochondria or chloroplasts are located at
a. the C-terminus of the precursor protein
b. amino acid position 173 in most mitochondrial and chloroplast proteins
c. the N-terminus of the precursor protein
d. At neither terminus.

9. Many peroxisomal matrix proteins are imported as
a. folded proteins
b. nascent chains in the process of completing their elongation
c. protein fragments that are spliced together within the peroxisome
d. unfolded proteins

10. Tom is an abbreviation for _____________________________________________________.

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